4.63. "The RiskMakeInput distribution ... may not be correlated."

I have a model that I developed in an earlier version of @RISK, and it simulated without incident. After upgrading, when I click Start Simulation I get the message

The RiskMakeInput distribution in cell location may not be correlated.

Or,

The RiskCompound distribution in cell location may not be correlated.

This worked before — why doesn't it work in the newer version?

It is true that the message is new in @RISK 6.3.0. However, it was always an error to try to correlate these functions; the only thing that's new is that now @RISK diagnoses the error.

Why can't special functions like RiskCompound and RiskMakeInput be correlated? When you click Start Simulation, if there are correlated distributions, @RISK draws all values for all correlated inputs up front, rearranges them appropriately to give the desired correlations, and then stores them for use during the sequential iterations of the simulation. (For details, see How @RISK Correlates Inputs.) That process breaks down with these two distributions. For example, @RISK can't predict what values a RiskMakeInput will take on during a simulation — in general, those values can't be known until the simulation is run. So @RISK has no way to reorder the values of a RiskMakeInput to produce the desired correlation.